To prevent unauthorized opening or tampering of containers holding food products, beverages, pharmaceuticals, and the like, it is highly desirable to provide a tamper-indicating arrangement which will clearly visually indicate that a container has been opened or tampered with. One type of tamper-evident seal that has been used in the past is a heat-shrinkable member, usually comprising heat-shrinkable thermoplastic material. Such a heat-shrinkable member is usually applied to an associated container in a generally cylindrical form, with heat thereafter applied to the member so that it shrinks and conforms to the associated container. The material from which the member is formed and the manner in which it is applied are selected such that upon attempted opening or opening of the container, the member is visually and permanently deformed to indicate attempted opening or opening. Copending U.S. patent application Ser. No. 451,401, filed Dec. 20, 1982, discloses a method and apparatus for forming spirally wound heat-shrinkable members which facilitate inexpensive and high speed formation of such tamper-evident seals.
While generally cylindrical heat-shrinkable members are suitable for application to many types of containers, their application to some types of containers can be problematical. The configuration of some containers is such that heat-shrinking application of cylindrical tamper bands thereto must be very carefully controlled to assure uniform shrinkage of the bands so that they properly embrace the containers. However, since tamper band application is preferably performed attendant to high speed packaging of products, it is frequently impractical or impossible to sufficiently control and monitor tamper band application to assure the desired interaction of the bands with their associated containers. Thus, it is desirable to provide a method of applying heat-shrinkable tamper bands or like members to containers so that it is possible to better control the heat-shrinking of the members into a configuration which will conform to the configuration of the containers to which the members are applied.
Another problem encountered with heat-shrink fitment of tamper bands or like members to containers relates to the manner in which they are heat-shrunk. After the members have been positioned in association with the containers, the members are shrunk by the application of heat, which is typically accomplished by passing the containers through a heat tunnel or like heat source so that the heat-shrinkable members are substantially entirely heated and shrunk into conformance with the containers.
While the above-described application technique is acceptable for applying heat-shrinkable members to many types of products, the use of this technique with some products and some containers is not acceptable. Specifically, some products are adversely affected when subjected to the heat of a heat tunnel or like heat source provided for shrinking the heat-shrinkable members into conformance with their associated containers. For example, a product such as frozen dessert topping can be unacceptably discolored when excessively heated. Even though such products may be maintained in a frozen state until just prior to application of heat-shrinkable members thereto, applying sufficient heat to the entire heat-shrinkable member for it to shrink into conformance with the product container can still result in the unacceptable discoloration or other adulteration of the product. Similarly, some types of containers cannot withstand the heat required to effect shrinkage of the heat-shrinkable members into that desired conformance with the containers.
Accordingly, it is highly desirable to provide a technique by which a heat-shrinkable member can be applied and conformed to an associated container with minimal heating of the container and its contents.